During a teaching session in a classroom the background noise may, firstly, prevent some of the participating students in hearing the voice of the teacher, since the signal to noise ratio in the classroom is low, and thereby reducing the possibility of learning. Consequently, the background noise may, secondly, cause the teacher to increase vocal amplitude thereby straining the teacher's vocal chord.
U.S. Pat. No. 5,818,328; discloses an area audio amplification system, which provides an improved signal to noise ratio and which is not susceptible to interference from frequency modulated signals. The system comprises a speech processor processing the audio signal to adjust signal level and response. In order to achieve this, the system comprises a low pass filter and de-emphasis network for limiting audio response to speech frequencies. The corner frequency of this network is 5 kHz. However, the system provides a time constant amplification of the audio signal, and therefore the background noise as such is not considered relative to the auditory sound, which primarily was attempted to communicate.
Further, American patent application no.: US 2003 0144847; discloses a sound masking system for masking out noise generated in large working environments. The system comprises a plurality of flat panel sound generators emitting highly effective and spatially uniform masking sounds within various zones. Hence the system provides masking of distracting noises in the working environment. Thus the system, as such, does not provide amplification of speeches, rather, oppositely reduces the noise relating to vocal communication.